Torpedo Attack on the USS St.
I had trouble with the commonly-accepted scenario from the outset. From my conversations with Kazuo Ueda (Vice Admiral, JMSDF, Retired, and senior surviving special submariner from the Imperial Japanese Navy) and Gou Okumoto (author of the Japanese reference book, The Complete History of the Special Purpose Submarine), my understanding was that the Ko-hyoteki class of special submarines were physically unable to fire both of their torpedoes in a close spread. These submarines were notorious for broaching to the surface after firing their first torpedo and the reason for this is obvious. Each of the two Type 97 torpedoes carried in the submarines that participated in the Pearl Harbor attack weighed approximately 2161 lbs. When the first torpedo left the tube, the sudden release of about a ton of deadweight from the extreme forward nose caused the bow of the 46-ton Ko-hyoteki to rise uncontrollably. This violent pitching of the bow often caused the sub to broach the surface, a dangerous characteristic of the design that was well known to the Japanese; in fact, the five Ko-hyoteki commanders selected to participate in the Pearl Harbor attack recorded this complaint in an 11-page "lessons learned" document compiled during their training at Kure. According to Ueda and Okumoto, it took at least 30, and sometimes as much as 90, seconds for the 2-man crew to adjust trim and regain enough stability to accurately fire the second torpedo. In addition to the violent pitch-up motion, the bow might also yaw while the crew left the controls to move lead weights around inside the hull to regain stability. Taken together, this notorious characteristic of the Ko-hyoteki class of submarines makes the kind of two-torpedo close spread reported by various crewmembers of the USS St. Louis an absolute impossibility.
Submarine at periscope depth, ready to fire the first torpedo.
Bow cap is blown clear by impulse air, and the torpedo leaves the tube.
The sudden loss of appoximately a ton of deadweight causes the bow of the submarine to pitch up violently. The forward momentum of the submarine exacerbates the motion. With the submarine originally at periscope depth, the conning tower immediately broaches the surface. The second torpedo cannot be fired until trim is regained on the submarine, a process that took at least 30 seconds but more often longer.
During a film interview with the Japanese network, NHK, St. Louis crewman J. D. "Doug" Huggins was asked about the reported twin torpedo tracks after a discussion about why it was impossible for the special submarine to fire two in a close spread. He responded, "You know, it might have been my assumption instead of actually seeing them. But I assumed that there were two wakes because I know that there are the stories that I’ve always read about the one caused the other to explode and that was....I didn’t hear that at first, I just heard that a few times a few years ago. Somebody surmised that it had to be that." However, when asked about whether he saw one explosion or two, he said, "Well, it was really one explosion....just, you know, it’s practically instantaneous when the one blew up, it blew the other one up." This uncertainty — two torpedo wakes, one explosion — is found throughout the St. Louis crewman accounts.